1. Field of the Invention
The present invention generally relates to a global system for mobile communication (GSM) terminal, and in particular to a system and method for storing short message service (SMS) messages in a GSM terminal.
2. Background of the Related Art
With the rapid popularization of mobile communications, usage of mobile communication terminals has greatly increased in comparison with usage of standard telephones in the home or office. A mobile communication terminal is a handheld device capable of wirelessly transmitting/receiving voice, character and/or picture information. These terminals not only perform general voice communication services but also various message transmission services and are generally classified as either a GSM (global system for mobile communication) terminal or a CDMA (code division multiple access) terminal.
A GSM terminal operates according to the European standard based on time division multiple access (DMA) techniques. More specifically, GSM terminals use a subscriber identity module (SIM) card to identify and authenticate a subscriber. The SIM card is a smart card which removably attaches to the GSM terminal and consists of a microprocessor and a memory. The memory stores personal information (e.g., authentication information) of an owner as well as information (e.g., telephone number and network number) for operating the terminal and SMS messages. A user can receive a request communication service after a SIM card is installed in a GSM terminal which supports a SIM interface and after passing a user authentication process.
FIG. 1 is a block diagram illustrating a general GSM (global system for mobile communication) system. This system includes GSM terminals 100-1, 100-2, a mobile switching center (SC) 110, and a SMS service center (SMSC) 120 connected to the MSC 110 in order to relay SMS messages between the GSM terminals 100-1, 100-2. The GSM terminals communicate with the MSC through base station subsystem 130-1, 130-2 respectively, and the SMSC 120 is connected to the MSC through a SMS gateway. The base station subsystems 130-1, 130-2 respectively include a base station controller (BSC) and plural base stations (BSs).
As shown in FIG. 2, each GSM terminal 100-1, 100-2 includes a SIM card 200 and ME (mobile equipment) 201, and is connected to external terminal equipment TE) 202 such as a workstation and a serial PC through an I/O connector 50. The ME 201 is a part separate from the SIM 200. The GSM terminal is constructed by combining the ME and SIM card 200 into the terminal. The ME also includes an internal memory which stores short messages and various information.
One method for storing short messages in a GSM terminal as previously described will now be discussed. Initially, an SMS message written in the GSM terminal 100-1 is transmitted to the SMSC 120 through the base station subsystem 130-1 and the MSC 110. The SMSC 120 discriminates a called number and transmits the received SMS message to the GSM terminal 100-2 through the MSC 110 and the base station subsystem 130-2. In transmitting the SMS message, the SMSC 120 transmits Class information for designating a position for storing a pertinent SMS message. The Class information may be Classified as one of four types:                1) Class 0: Display only        2) Class 1: Store a SMS message in the ME (internal memory of the terminal)        3) Class 2: Store the SMS message in the SIM card        4) Class 3: Store the SMS message in the TE        
Class 0 information is transmitted for only displaying the SMS message. Class 1 information is transmitted for storing the SMS in the ME 201. Class 2 information is transmitted for storing the SMS in the SIM card 200. And, Class 3 information is transmitted for storing the SMS message in the external TE 202. The SMSC 120 can transmit SMS messages without designating SMS Class information.
When the SMS message is received from the SMSC 120, the GSM terminal 100-2 checks whether there is Class information in the received SMS message. When Class information is in the received message, the SMS message is displayed or is stored in one of the SIM card 200, the ME 201 and the TE 202 by referring to the pertinent Class information.
When no Class information is in the received SMS message, the GSM terminal stores the SMS message according to a preset storing priority order. For example, the GMS terminal 100-2 stores the received SMS message in the SIM card 200 first, or, the GSM terminal 100-2 stores the SMS message in the ME 201 only when a message storage of the SIM card 200 is full.
As previously described, when the SMSC does not transmit Class information, the GSM terminal stores the received message in the SIM card first according to the preset storing priority order. However, when the storage of the SIM card is full and an SMS message having Class 2 is received, the GSM terminal can no longer receive the Class 2 type SMS message even though there is sufficient storage space in the internal memory of the ME. In addition, when the internal memory of the ME is full, the GSM terminal cannot receive the SMS message if a SMS message designated in Class 1 is received.
In order to solve the above-mentioned problem, the terminal user is forced to check SMS messages stored in the terminal and delete unnecessary messages, which results in significant inconvenience to the user.
Thus, in the conventional method for storing SMS messages in a GSM terminal, it is impossible to store SMS message efficiently in a request storing region based on SMS Class, and accordingly reliability of the SMS service may be lowered due to the message reception rate lowering problem.